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FAQ – Frequently Asked Questions

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Questions about Photovoltaics & Technology

What are monocrystalline modules?

Monocrystalline solar cells for photovoltaic systems are manufactured from the semiconducting material silicon by applying a very complicated and costly process. Because of their high share of silicon, they have an energy efficiency factor of up to 20 per cent. Based on a cost-benefit calculation, the dark-blue to blackish coloured monocrystalline modules are currently the most effective solar cells available.

Monocrystalline solar cells can last to approx. 30 years. The use of monocrystalline modules is recommended if you want to attain the highest possible output from a small area.

What are polycrystalline modules?

Like monocrystalline cells, polycrystalline solar cells are manufactured from silicon. But in this case, the silicon used is not quite as pure as that of monocrystalline cells. Manufacturing the module is less complicated which is down to the lower energy requirements. Because of the cheaper manufacturing procedure, the bluish coloured polycrystalline modules currently offer the best price-performance ratio and are the most frequently installed modules. These modules have an efficiency rating of about 15 per cent. While polycrystalline modules show a better environmental performance than monocrystalline cells, they also have a lower efficiency, which is why they are frequently used for bigger photovoltaic plants that need not depend on the output of every single solar module.

What do the terms Wpeak / KWp / Wp / peak mean?

KWp is a common term used in photovoltaics to describe the power output of solar cells. The term kWp refers to the system's peak capacity achieved under optimum conditions. The required standard test conditions (STC) refer to a radiation intensity of 1,000 watt/m2 at operating solar cell temperatures between 20 and 25 °Celsius. A plant should additionally be positioned in such a way to allow sunrays to strike the solar modules at an angle of 48 degrees.

What happens if there’s a power failure?

The transformers and solar inverters, as well as the online surveillance electronics and system, require electricity, also during the night. By installing an UPS unit (uninterrupted power supply), video surveillance continues long enough to be able to repair any damage. Any failure of the other systems will lead to no damage or serious problems whatsoever.

The solar inverter is an automatic facility that interrupts feed-in in the event of a power failure within the shortest of time. An irradiation sensor installed on top of the system estimates the loss of electricity yield, and the operators receive appropriate compensation either from the yield loss insurance or from the grid operator.

What is the plant’s service life?

Since photovoltaics is a comparatively young technology, meaningful long-term experience is not yet available. But there are still some early PV roof-top models in operation which have already reached a service life of 30 years. In the course of the technology's development, a number of teething troubles were solved. Ancillary components such as the foil, lamination, the frame or the junction box on the back, for example, used to be extremely susceptible to weather damage, particularly in the early days of PV. As the "energy generating" silicon coating does not wear off, there is no wear whatsoever inside the elements. The PV modules must be able to deal with extreme variations in temperature and weather impact such as precipitation, wind or snow. They are also constantly exposed to the effects of salt, dust and sand. In this respect, the technology has advanced dramatically, and the estimated life time of the modules is now significantly longer than 30 years.

If soiled modules, for example, do lead to a drop in output, this merely means reduced efficiency but not a complete loss. The solar inverters in use today have an estimated life time of around 20 years. If there is a fault, it is often only the PCB or other components that need replacing. The other parts such as wiring, the substructure or the fencing are barely subject to wear at all.

What happens if it is cloudy?

Depending on the module technology in use, the solar panels have different ways to handle weak light. There is no such thing as a universal module that can cope optimally with all types of solar radiation - be it summer midday sun or weak radiation on an afternoon in winter. Based on the forecast conditions on site it is accordingly always necessary to consider carefully which module technology would be best for each individual situation. Obviously, the different prices for the varying technologies will also be a crucial factor. But PV modules can generally also utilise the diffuse radiation from cloudy skies. The brighter it is, the higher the radiation - whether the sky is cloudy or clear.

The key component of a solar cell is silicon, a product made of melted sand. Silicon conducts energy only if there is direct or indirect solar radiation. Every single solar cell in a PV module has a phosphorus coating on the front and a boron coating on the back. The different coatings produce an electric imbalance which constantly requires to be balanced out. The silicon in the middle serves as a semiconductor medium, allowing the energy to flow in the form of direct current to the connected device during sun exposure.

What does efficiency factor (degree of efficiency, performance ratio) mean?

The efficiency factor, also known as the PV plant's performance ratio, uses several factors to determine the efficiency of the entire plant. The used components, the location on a slope, the orientation to the south, the substructure's tilt angle with respect to the horizon as well as the wire cross sections and lengths are all taken into account.

The entire plant's efficiency factor is usually around 80% (+/- 5%). I.e. it specifies how much of one kWh of sun radiation is converted into electrical energy in the grid. The efficiency factor of the currently most common PV models is between 14 and 17% in monocrystalline modules and between 7 and 10% in thin-film modules.

How does an inverter work?

The inverter is the heart of every PV plant. This is where direct current from the solar modules is converted into standard alternating current. The generated alternating current can then be fed into the grid of the respective electricity supplier via an export meter. The compensation for the produced energy is based on the energy supplier's feed-in tariff.

How is a PV plant connected up to the grid?

The individual modules are connected in series and the "strings" are bundled together using cables with higher cross sections. After that, the direct current is converted into alternating current using the inverters. At so-called transfer stations, there are power transformers which adjust the voltage to suit the required mains voltage in the public grid. Usually this will be medium voltage between 20 and 35 kV depending on the country.

What components does a (grid-connected) photovoltaic plant consist of?

To erect a photovoltaic facility, fencing, wiring, solar inverters and PV modules are needed. Further components are the substructure, the power transformers, a low-voltage distribution network and a control unit. Optionally, online monitoring technology with a video surveillance system can be used as a security measure.

How are the PV systems mounted?

There are as many ways to mount the systems as there are systems themselves (flat roof, sloping roof, facade, ground-mounted or carport systems). You can choose between an insertion system and a system with clamps. The insertions system reduces installation time significantly compared to conventional clamping systems. Apart from that, the insertion method is kinder to the material and easier to maintain, since it produces no mechanical tension in the modules or module frames, and no screws are applied to the modules.

To fix the module tables in the ground, EEPro exclusively uses the proven pile-driving method based on the crash barrier principle. Using mobile pile-driving equipment to suit the terrain and a lifting system, a small hammer is dropped on top of the head of the profile over and over again. In doing so, the pile made of hot-dip galvanised steel is driven into the ground.

But does its production not use much more energy than the photovoltaic facility could ever generate?

In the early days of PV, this was indeed true, but the swift advancements made in this field have reduced the amount of energy used for producing PV plants to a minimum. Due to its long service life of 25 years, the energy used for its production is amortised after as little as ten years. Apart from that, both the aluminium substructure and the modules (glass and silicon) and the wiring (copper) can all be reused.

Questions about EEPro’s Services

Does the plant need to be cleaned?

Basically, the solar panels we use are classified by their manufacturer as "self-cleaning" due to their glass structure and the special coatings applied. The optimum tilt angle with respect to the horizon (in Germany this is 30°) allows self-cleaning by rain. Heavy rainfall automatically washes off leaves, pollen and other contamination.

Bird droppings or exhaust gas emissions from industrial plants, on the other hand, are much more resistant. That is why we periodically check the cleanliness of our plants on scheduled solar farm inspections. If necessary, we clean the modules at extra cost. This is done after analysing the costs and the additional yields to be achieved following cleaning.

How high are the maintenance costs?

The yield calculation already takes into account the amount of maintenance costs in the current costs. Basically, however, the maintenance costs, too, are country-specific. For solar farms in Southern Germany, EEPro GmbH takes over maintenance work and is therefore able to offer lower tariffs. For solar farms abroad we look for reliable partner companies, where possible, such companies which were also involved in the project during its construction phase.

For Germany, about 15-20 euros per kWp and year are estimated. For international projects, about 20-30 euros per kWp and year are calculated. The high share of costs for lawn maintenance should not be underestimated. EEPro attaches great importance to ensuring that a plant not only is kept in optimal technical condition, but also remains presentable throughout its operating life.

Is a construction permit needed?

As the plant is a physical structure at least one construction permit is needed, depending on the previous nature of the property. In Germany, for example, a change in the land development plan (Flächennutzungsplan) and the more detailed zoning plan (Bebauungsplan) will be needed beforehand.

How is the plant insured?

During the construction phase, a construction risk insurance is taken out. Insured are primarily construction damages in relation to third parties and theft (despite fencing). For plants which EEPro itself manages in the context of commercial administration, all-risk insurance is taken out during the operation term. This insurance covers damages such as strong wind, hail, floods, fire, theft, vandalism and also loss of profits. From the second day onward, the insurance covers loss caused by plant failure or theft, etc.

Questions about the Company

When was EEPro founded and how many employees does the company have?

EEPro GmbH was founded in 2007. In Germany, we currently have 12 employees - another 15 experts are employed in the context of our international projects. During the construction phase of a 5-MW solar facility, for example, there will be around 50 temporary staff from external partner companies working for EEPro.

In which countries has EEPro already implemented solar projects?

So far, EEPro has installed solar farms in Germany, Italy, Spain, Bulgaria, the Czech Republic, South Africa and in Slovakia.

How much capacity has EEPro already installed all over the world?

According to the latest figures, EEPro has installed 25 MW, but this figure will rise to 35 MW by the end of 2011 due to the completion of projects currently underway. For 2012, a sales volume of further 20 MW is planned. If our current plans in South Africa area realised according to our expectations, around 300 MW will be installed by the end of 2013.

Questions about Investment

What rate of return may I expect if I invest in a solar project?

The rate of return from a solar farm depends on many different factors. Depending on the country-specific subsidies, the financing arrangements and conditions, the solar radiation, the kind of technology employed, the depreciation allowances, taxes, plant size, etc. you can expect rates of return between 7 and 20%.

Are there government subsidies?

The regulations vary state by state. In most countries, a government subsidy is granted. It is usually paid to the solar farm operator/owner in the form of a higher feed-in tariff for the generated energy. The entity granting the subsidy varies too: Some countries collect the costs for the subsidy straight from the electricity rate payers (e.g. Germany). Other governments finance the subsidy by general tax revenues.

Thanks to a high general electricity price and high yearly insolation levels, a few countries are already capable of producing electricity at competitive prices in the regional market.

Thanks to rising electricity prices and falling plant costs, grid parity in Germany is expected to be reached by 2015.

Who pays the energy compensation?

(For more details, see question: Are there government subsidies?)

This varies by country. In Germany, the electricity customer pays the subsidy: An average household pays the energy feed-in tariffs with about 5% of its electricity costs. Yet compared to the high follow-up costs for nuclear power imposed on the public, the amount households pay for energy feed-in tariffs is in fact very small.

How much compensation does one get for the produced electricity?

This, too, varies by country and the payments are constantly changing. On the one hand, the state wants to encourage the use of photovoltaics, but on the other, it is not prepared to "oversubsidise" the technology. But compensation is not the only crucial factor. In a country like South Africa, which has solar radiation of about 2,000 kWh per year and square metre of level area, a tariff of 20 cent/kWh is more attractive than a tariff of 25 cent/kWh in Germany (1,200 kWh per year and square metre of ground).

What happens if the Renewable Energies Act (EEG) is changed?

If the Renewable Energies Act is changed, existing PV plants that are already supplying electricity to the grid will not be affected in any way. These plants have a right of continuance, i.e. they are operated under the same legal conditions that were applicable at the time they went into operation. Changes with retroactive effect on the level of compensation are incompatible with constitutional law. But the legislative body does reserve the right to suggest future adjustments to the compensation levels for new PV facilities.

What fluctuations have an impact on photovoltaics?

Solar variation over a year is relatively low (plus/minus 10%), because even if it the skies are cloudy, the plants still generate electricity. In comparison, wind power may fluctuate up to 30% around the long-term average. The constant electricity yields and the feed-in tariff fixed for the next 20 years make solar plants comparatively safe, economically and ecologically sustainable capital investments.